The invention relates to an optical method for detecting the presence of defects in thin films.
Thin metal, polymer, and semiconductor films are common in microelectronic, optical, biomedical, and aerospace devices. They are typically intricate devices with many microscopic features. For example, in a silicon wafer there may be vertical "posts" of metal running through the insulating oxide layers, providing electrical connections between different metal layers. Also common are "trenches" filled with metal embedded within the oxide layers. In any case, during or after fabrication steps, defects in the desired features may occur. For example, a trench may not have been properly etched or may not be completely filled with metal. A post may be unfilled, leaving a void rather than a conducting region. Such defects will limit the performance of the final device, in some cases making them inoperable.
Ideally, a defect is detected before the device containing the defect is completed. This prevents unnecessary processing of the defective device, thereby saving time and money. Furthermore, the causes of defects can be more easily determined once the defects are detected and characterized. However, defects are usually buried within devices making their detection difficult.